Materials with high dielectric constant are desired for many modern electronics applications that involve a capacitor-like element, including DRAM and transistor gates. High dielectric constant values can correlate with small band gap, thus the requirement that the dielectric has a sufficient band gap (typically >˜3 eV) makes it difficult to increase dielectric constant by purely chemical means.
Rutile materials, such as rutile titanium dioxide (TiO2), have been used as dielectric materials for high dielectric constant applications. TiO2-based dielectric materials have the potential to exhibit relatively high dielectric constant values. However, the effective dielectric constant, keff, typically remains below 100.0 (e.g., 80-90).
However, high dielectric constant values have been discovered for TiO2 single crystals when measured along a tetragonal axis (i.e. along the [001] direction). For example, a single crystal rutile TiO2 material at room temperature, and frequencies in the 102 . . . 106 Hz range, has been found to exhibit dielectric constant values of κ⊥=86 and κ∥=170, when the field is applied respectively perpendicularly and parallel to [001].
As such, the effective dielectric constant values exhibited in semiconductor devices suggest that for a typical modern semiconductor manufacturing sequence, the materials crystallize in a manner such that the effective dielectric constant is reflected by the smaller dielectric constant κ⊥ value. At best, a polycrystalline rutile film with randomly oriented crystallites may be utilized, in which case, the effective dielectric constant κeff value is an average of κ⊥ and κ∥ with a twice larger weight given to the smaller dielectric constant κ⊥ value. The exact form of averaging that describes the effective dielectric constant value, κeff, depends on crystal microstructure, but an approximate value can be calculated using the effective medium approximation, which for randomly oriented crystallites in rutile TiO2 can yield κeff≈110. In fact, the actual κeff values of polycrystalline rutile TiO2 with randomly oriented crystallites may be lower than 110 due to imperfections present in the TiO2 polycrystal.
Therefore, there is a need to increase the effective dielectric constant values of dielectric materials within semiconductor-based capacitive devices.